1. Technical Field
The present invention relates in general to integrated circuitry and, in particular, to dispensing of chip underfill.
2. Description of the Related Art
An integrated circuit (IC) chip is conventionally mounted to a carrier or substrate in one of two ways. According to a first technique, the IC chip is mounted with its electrically conductive pads oriented upward and with wire bonds connecting the pads to pins on the outside of the carrier, which in turn electrically connect the IC chip to external circuitry. Alternatively, the IC chip can be mounted with its pads oriented downward as a so-called “flip chip”, in which case solder bumps (also referred to as a Controlled Collapse Chip Connection (C4)) are used to directly connect the chip pads to the associated external circuitry.
The connection between the flip chip and the carrier is vulnerable to mechanical stress, which if great enough, can cause at least one C4 connection to fail. Consequently, in most cases, flip chips are underfilled with an electrically insulative adhesive to enhance the strength of the mechanical connection between the flip chip and the carrier.
Currently, the most common technique for applying underfill to a flip chip is to dispense the underfill material with a needle dispenser along one or more edges of the IC chip and to rely upon capillary action to cause the underfill material to flow beneath the IC chip and around the solder bumps. A disadvantage of this technique of applying underfill is that the underfill material can form a wide fillet on one or more sides of the IC chip, forcing a minimum spacing to be observed and reducing the component density that can be achieved on the carrier.
An alternative technique that has been proposed is to underfill IC chips from the backside of the carrier via a through hole formed in the carrier. However, this presents a significant design and fabrication challenge for large chip carriers (e.g., large ceramic multi-chip modules (MCMs)), which may have numerous layers and are designed to carry large number of chips.